Just a thought. If your PV array was capable of lets say 1000Watts and you fitted a 100/20
Victron unit. All that would mean is that the charge current would never exceed 20amps? I know that your potential
solar capacity would be wasted, but that 1kw array would be able to produce 100watts more often that 1kw. Or am I misunderstanding how it works?
What would happen [
with the Victron Controller] is any power generated that would exceed the limit of the controller gets discarded. I did a rough chart to illustrate this, posted below, with Amps on the vertical axis.
So if the controller was a 20A unit, as the potential output current rises above 20A, anything above that is lost and the charge current goes flatline.
Does this matter? Well, you are potentially wasting charging capabilty but some things to consider.
1) The
Solar Array only peaks for a very short time in the day; plus even that peak will only happen for a few months of the year.
You may have a large array installed just so you get better harvesting outside the peak times but don't actually have a need to achieve 100% of the arrays capabilty.
2) Depending on your
battery type, capacity and level of charge, even if you had a 30A controller and your array COULD produce 30A, the
battery may only be able to accept 20A or even less, so you may get the benefit of a the higher capacity controller for a very small time.
Whether it is worth undersizing depends of how much you want to achieve (remember it is rarely good to charge a Lead Acid
battery at over 20-25% of its capacity, so a 100Ah
battery would not want more than 25A anyway); Plus the cost could be a factor - jumping up a level could potentially be quite pricey and if you are only just under the arrays maximum limit it may not be worth it (taking factors above into play)?
That might not be the case. My Votronic MPPT manual clearly specifies Watts and Amps as
solar input limits not as charging output limits. For example the 250 model has a
solar input limit of 250W and 15A. An overloaded unit might blow a
fuse but it might possibly burn out the electronics as well. In my opinion very much not worth the risk.
I don't know about the Votronic controller, but the
Victron Controllers are designed to work as I describe above and there is no issue having a 'oversized' array connected to it.